1,721,021 research outputs found
Modeling contaminant propagation in a fractured and karstic aquifer
No full textModeling flow and transport of pollutants in fractured and karstic aquifers remains an open issue. In fact, a completely adequate model for them has not been developed. These aquifers are highly vulnerable to groundwater contamination. Karst conduit system permits a rapid transport of pollutants, often under turbulent conditions and traveling long distances. Moreover, the cavities filled by residual dissolution products delay the propagation of contamination principally by means of sorption processes. The classical equivalent porous model paradigm does not permit to take into account the discrete nature of these aquifers. In this context, the reconstruction of a detailed geological model is very important in order to extend the knowledge on fluid flow and solute transport phenomena. This permits, consequently, to choose a plausible conceptual model with state variables and boundary conditions more adequate than the classical equivalent porous approach. The present work studies the area of an ex Gasometer heavily contaminated by hydrocarbons. In this area, a pump & treat system has been designed approximating the nature of aquifer to a homogeneous isotropic porous medium. The work focuses on the importance of the realization of a detailed geological reconstruction to be implemented in a flow and transport model in order to interpret the dynamics of the flow field and the transport of contamination. The obtained results have proven to be coherent with previous studies in that they show that the flow field and the transport of contaminants depend primarily on karst network architecture. © by PSP
Modeling contaminant propagation in a fractured and karstic aquifer
No full textModeling flow and transport of pollutants in fractured and karstic aquifers remains an open issue. In fact, a completely adequate model for them has not been developed. These aquifers are highly vulnerable to groundwater contamination. Karst conduit system permits a rapid transport of pollutants, often under turbulent conditions and traveling long distances. Moreover, the cavities filled by residual dissolution products delay the propagation of contamination principally by means of sorption processes. The classical equivalent porous model paradigm does not permit to take into account the discrete nature of these aquifers. In this context, the reconstruction of a detailed geological model is very important in order to extend the knowledge on fluid flow and solute transport phenomena. This permits, consequently, to choose a plausible conceptual model with state variables and boundary conditions more adequate than the classical equivalent porous approach. The present work studies the area of an ex Gasometer heavily contaminated by hydrocarbons. In this area, a pump & treat system has been designed approximating the nature of aquifer to a homogeneous isotropic porous medium. The work focuses on the importance of the realization of a detailed geological reconstruction to be implemented in a flow and transport model in order to interpret the dynamics of the flow field and the transport of contamination. The obtained results have proven to be coherent with previous studies in that they show that the flow field and the transport of contaminants depend primarily on karst network architecture. © by PSP
An integrated modeling approach for a contaminated fractured limestone aquifer: the area of ex Gasometer in Bari (Italy)
No full textAn integrated flow and transport modeling approach for a contaminated fractured limestone aquifer: the area of ex Gasometer in Bari (Italy)
No full textThe present study concerns the dismissed industrial area of ex
Gasometer, located in the city centre of Bari (Italy), where the aquifer is
constituted mainly by extremely fractured limestone formations and is heavily
contaminated by petroliferous substances, due both to the past industrial
activity and to the subsequent removal of the installation and the tanks.
In the area different campaigns of investigations have been carried out,
together with pilot tests of Pump &Treat and air sparging. In previous studies
carried out on the area, the analysis of the possibilities of remediation of the
aquifer has considered flow and solute transport in an equivalent porous
medium, and the anisotropy of the fractured formation was synthesized in a
coefficient of hydraulic conductivity obtained by a geostatistical study.
The distribution of hydraulic heads coming from the flow simulation turned
out to be adherent to reality but the velocity fields obtained proved to be
considerably lower, affecting predominantly the propagation of the
contaminants.
This paper has taken into account the uncertainty connected to the pronounced
spatial heterogeneity due principally to the fractured and karstified nature of
the soil, to the complexity of the state of contamination due to accidental
episodes happened in the area, and to the dishomogeneity of the results
obtained from campaigns of investigations carried out with different
procedures. A system based on the fuzzy logic has been implemented,
composed by different blocks of inference interacting among themselves that,
on the basis of a process of inverse modeling, has permitted to characterize the
source of contamination, to calibrate and/or estimate the flow, transport and
biodegradation parameters. For the automated tuning of the fuzzy system the
algorithm of Simulated Annealing has been implemented. A more effective
simulation has been obtained in the present study through the application of
the approach of Dual Domain Mass transfer, able to describe the solute
transport in a fractured medium. The three dimensional transport model
realized on the basis of the computer code Seam3D considers also the
presence of possible sources of contamination by NAPL and simulates direct
degradation processes.
This model has allowed to study the dynamic behavior of the aquifer and has
permitted to realize that it is necessary to remove the NAPL source of
contamination in the soil, still active, before carrying out any interventions of
remediation of the aquifer
Modeling and analysis of the effect of faults on the flow and saltwater intrusion phenomenon in a coastal aquifer
No full textThe tectonic structure of an aquifer can influence the dynamics of groundwater flow with effects on the aquifer's vulnerability. In an area located in Salento Peninsula, characterized hydrogeologically by a multi - aquifer system, superimposed on the deep aquifer, that prove to be heavily salsified even in the internal areas, a qualitative deterioration of the shallow aquifer used for irrigation starts taking place. A joined analysis of the dynamics of groundwater circulation in relation to the morphotectonic asset of the area, reconstructed on a detailed geologic model implemented on a density dependent flow model, has pointed out the influence of the tectonics on groundwater flow behaviour and on the exchange phenomena between the two aquifers, explaining therefore the increment in groundwater salt concentration
Checking simulations of a geolithological model obtained by means of nested truncated bigaussian method
No full textCharacterizing the spatial distribution of major lithotypes and their relationships is a key aspect in the process of hydrogeological modeling of aquifers in that assignment of lithotypes-specific hydraulic and hydrochemical properties requires the knowledge of the layout of the lithotypes themselves. Truncated bigaussian simulation is a procedure derived from the truncated Gaussian model, used to simulate random sets, and, in particular, variable geological characteristics, expressed as categorical variables. Anyway, in cases of many lithotypes having not homogeneous spatial behaviors, this methodology might not explain at best the relations existing among the lithotypes themselves; a more general method is therefore required to represent this variability. In this paper, that concerns a site whose geologic asset has already been reconstructed, in order to better characterize the aquifer geolithological architecture, nested simulation for a macro-unit of the previously realized geolithologic model has been carried out, together with a check phase of the results obtained by the mentioned simulation. The proposed methodology can represent a useful instrument for the modeling of complex geological layouts other than in the detailed characterizations of hydrogeological studies, for a better interpretation of the complex phenomena that take place in groundwater circulation and contaminant propagation
Stochastic geolithological reconstruction coupled with artificial neural networks approach for hydrogeological modeling
No full textWhen simulating fluid flow and solute transport a more accurate modeling of the lithologic, geological and structural characters of an aquifer is of extreme importance in order to improve the reliability of the numerical simulations. On the other hand the information available for the setting up of a hydrogeological model is subjected to ambiguities due to not univocal interpretations or to uncertainties linked to the methodologies of measurement of the variables of interest. Therefore, hydrogeological characterization of heterogeneous aquifers, if carried out up to a high degree of detail, should not identify a univocal model but a set of "equifinal" solutions. In the present paper the application of Artificial Neural Network approach coupled with a Nested Sequential Indicator simulation has allowed to obtain the distribution of hydrogeologic parameters that are not only conditioned by the in situ measured values but also by the soft information coming from geolithology. The results show a fairly good relationship between parameters such as Transmissivity and Storage coefficient and the geolithologic architecture of the examined aquifer
An efficient random field generator for the implementation of a hydrodynamic model of a contaminated fractured aquifer
No full textAnalysis of gravel back-filled borehole heat exchanger in karst fractured limestone aquifer at local scale
Full text linkIn designing and sizing of borehole thermal energy system, natural groundwater movement and temperature driven flow have a great importance on the borehole heat exchanger efficiency. The efficiency of double U – tube arrangement in gravel – backfilled borehole installed in a fractured limestone aquifer has been analyzed by means of three – dimensional numerical simulations. The numerical model is representative of 1 m deep of gravel back – filled borehole surrounded by the fractured aquifer. Several simulations have been carried out in order to evaluate the effect of aquifer parameters and boundary conditions on heat exchange efficiency by varying the mean temperature within the double U - tube. The fractured limestone aquifer of the industrial area of Bari (Italy) has been chosen as field site in order to identify the aquifer parameter range and the respective combinations.
The results highlight that borehole thermal energy system efficiency is strictly dependent on aquifer transmissivity and groundwater Darcian velocity. The conducted analysis shows that, under lower Darcian groundwater flow and lower aquifer transmissivity, heat transfer efficiency increases at least by 25% compared to stagnant water, whereas heat transfer in the aquifer is governed by heat conduction. The increase of aquifer transmissivity induces the thermosiphon effect enhancing heat transfer processes both in the gravel back-filled borehole and aquifer. At higher values of groundwater Darcian velocity (> 0.1 m/d) advection due to groundwater
flow is not negligible and mixed with free convection enhancing heat transfer further. Based on the results, discussion on the performance and environmental constraint of gravel back – filled borehole at field site has been presented
Stochastic geolithological reconstruction coupled with artificial neural networks approach for hydrogeological modeling
No full textWhen simulating fluid flow and solute transport a more accurate modeling of the lithologic, geological and structural characters of an aquifer is of extreme importance in order to improve the reliability of the numerical simulations. On the other hand the information available for the setting up of a hydrogeological model is subjected to ambiguities due to not univocal interpretations or to uncertainties linked to the methodologies of measurement of the variables of interest. Therefore, hydrogeological characterization of heterogeneous aquifers, if carried out up to a high degree of detail, should not identify a univocal model but a set of "equifinal" solutions. In the present paper the application of Artificial Neural Network approach coupled with a Nested Sequential Indicator simulation has allowed to obtain the distribution of hydrogeologic parameters that are not only conditioned by the in situ measured values but also by the soft information coming from geolithology. The results show a fairly good relationship between parameters such as Transmissivity and Storage coefficient and the geolithologic architecture of the examined aquifer
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